1. Field of the Invention
This invention relates to the field of communication networks. In particular, the invention relates to a method and apparatus for roaming in a mobile communications network.
2. Description of the Related Art
A mobile communications system may include various systems between which a subscriber may wish to travel. Often a subscriber is associated with a particular system and when the subscriber is present in a region serviced by another system, the subscriber is considered to be roaming. A subscriber's home system is typically a system for which the subscriber is registered. Several techniques allow mobile subscribers to roam into systems different from the subscriber's home system. An example is the IS-41 based system.
Some prior art systems use home location and visited location registers (HLR/VLR) and even dedicated switching networks for mobile subscribers. A disadvantage of some prior systems is the possibility of single point of failure, the need for a dedicated signaling network, the need for central coordination between entities entering into roaming agreements and difficulties in billing.
Some methods in the prior art rely on explicit rules for determining the home location of a roaming subscriber and how to handle a call to and from such a subscriber. Typically in such applications these functions are carried out by interrogation of an HLR. Such an approach introduces complexity and delay. Prior art methods also may require additional signaling traffic to establish correct billing for each call since the path may go through a different exchange than the subscriber's home exchange. Such additional signaling may be complex.